1. Industrial Useful Field
This invention relates to an improvement in a mold for lead casting which is used in casting of grids or spines for lead battery and in casting of lead parts for lead battery.
2. Prior Art and its Problem
In casting the grids and spines for lead battery; mold for lead casting is used at present, which are provided with thermal insulation, air venting ability and mold releasing ability by coating a so-called "lubricant" composed mainly of cork powder on metal surfaces made of cast material through means of the spraying method.
However, since the lubricant is composed mainly of the cork powder, it is carbonized by thermal decomposition when contacting unceasingly with molten lead heated to 500.degree. to 400.degree. C. Further, its thickness is decreased by being pressed by a pressure of the molten lead due to an elasticity of the cork layer. The lubricant layer gradually loses its thermal insulation, so that solidification of molten lead will commence and so-called cross-grain will be produced before completion of flow of molten lead i.e. before a time required for the molten lead to spread into the entire cavity to be filled has elapsed, if the same conditions as the initial fresh lubricant are set as they are. When the thickness of the lubricant layer becomes small, a weight of grid will become scattered because a weight of grid of product will increase gradually.
When a worker judges that the lubricant has deteriorated as described above, the former coated layer should be removed by brushing and a new layer should be sprayed again. However, since it requires a long term of experience to learn the skill of coating the lubricant to its level of practical use, a worker employed in casting process must be a skilled person who has achieved complete mastery. Namely, the worker must acquire such techniques that a coating thickness is to be altered in consideration of the grid frame thickness, basin, air venting etc., and air venting grooves are to be formed in portions where air is hard to be vented. Accordingly, restrictions are placed in freely posting workers within a factory from the existing state of things. Further, it is difficult to invite skilled workers in a newly built factory.
A time until the lubricant is completely deteriorated or a number of casting shot can not be determined unconditionally because it depends on a mixing/prescribing method of cork powder, a kind of alloy, a thickness of grid, a sectional area of frame and mold cooling method etc. In case of antimony alloy, it is generally said that three or four hours will be required for that purpose. Therefore, two times of recoating per day are necessary. In case of calcium alloy, it is said that three times bf recoating per day are necessary. It requires 20 to 30 minutes for a skilled worker to perform this work, and the casting machine should be shut down during this period. The sum of shut-down time per day reaches 40 to 90 minutes on every casting machine.
This lubricant coating work generally consists of an air spraying method, in which the cork powder dissolved in water glass, glue or phosphoric acid base binder solution is sprayed onto a heated metal surface; so that the cork powder scatters around the machine to contaminate its periphery and the method does not provide a good work environment.
As described above, the lubricant has a function necessary for enabling the casting. However, if there exists some other method for enabling the casting without using the lubricant, it can not be doubted that the casting work can be carried out effectively in all respects.